Cytochrome c-555 and iron-sulfur-proteins of the non-thiosulfate-utilizing green sulfur bacterium Chlorobium vibrioforme

Abstract

The non-thiosulfate-utilizing green sulfur bacterium Chlorobium vibrioforme contains only one soluble c-type cytochrome (c-555) besides two rubredoxins and ferredoxin. These electron transfer proteins were highly purified by ion exchange chromatography and gel filtration.

Cytochrome c-555 is a small and weakly basic hemoprotein with an isoelectric point at pH 7.3, a redoxpotential of + 80 mV, and a molecular weight of 11,500 (±500) determined by electrophoresis on sodium dodecylsulfate polyacrylamide gel, and of 11,000 by gel filtration on Sephadex G-75. Cytochrome c-555 shows maxima at 412.5 nm in the oxidized form, and three maxima in the reduced state (α-band at 555 nm with a shoulder at 551 nm, β-band at 523 nm, and γ-band at 418 nm). The best purity index (A₂₈₀/A₄₁₈) obtained was 0.15.

The two rubredoxins (rub I and rub II) are acidic small proteins and both have the same molecular weight of 8,100 estimated by gel filtration on Sephadex G-75 and show the same maxima at 370 nm, 492 nm, and 575 nm in the oxidized form but differ only in their isoelectric points at pH 2.9 (rub I) and at pH 2.7 (rub II). The best purity index obtained (A₂₈₀/A₃₇₀) was 3.27 for rub I and 3.57 for rub II respectively. Both rubredoxins contain one iron atom per molecule.

Ferredoxin is also an acidic protein with an isoelectric point at pH 2.5 and shows maxima at 300 nm and 380 nm in the oxidized form.